Multiple plate clutch device

ABSTRACT

A multiple plate clutch device is provided to conserve space. In a reverse hydraulic brake device  7,  a plurality of teeth  35  is formed next to one another in a circumferential direction in an inner peripheral surface portion  31  of a transmission case  21.  A plurality of first brake plates  24  includes engagement teeth  41, 42.  The engagement teeth  41, 42  engage the plurality of teeth  35  on the inner peripheral surface portion  31  such that the plurality of first brake plates  24  is axially movable and non-rotatable relative to the inner peripheral surface  31.  A plurality of second brake plates  25  is disposed to alternate axially with the plurality of first brake plates  24.  A piston  22  pushes the plates  24  and  25.  Return springs  28  are disposed within deep grooves  37  that are between the teeth  35  and the inner peripheral surface portion  31.  The return springs  28  urge the first plate  29  that is closest the piston  22  towards the piston  22.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a multiple plate clutch device.More specifically, the present invention relates to a multiple plateclutch device having a return spring for returning a piston.

[0003] 2. Background Information

[0004] Generally speaking, conventional multiple plate clutch devicesare equipped with a plurality of first and second plates arrangedalternately in an axial direction and a piston that is driven byhydraulic pressure. Conventional multiple plate clutch devices press thefirst and second plates together. Multiple plate clutch devices are usedin automatic transmissions and also function as a brake. The multipleplate clutch device is also provided with a return spring for returningthe piston and releasing the clutch.

[0005] A plurality of coil springs, for example, is used as returnsprings. The coil springs are disposed in a circle with one endsupported by a retaining plate and another end abutting the piston. Theretaining plate receives a load from the piston by means of a snap ringfixed axially to a wall surface thereof. As a result, when hydraulicpressure does not act on the piston, the load applied by the returnspring returns the piston and releases the encasement of the clutch.

[0006] Since the return springs arrangement just described is providedwith a retaining plate and a snap ring, the number of parts increasesand causes the multiple plate clutch device to be relatively expensive.Furthermore, the axial dimension of the device becomes large because acertain amount of space must be secured in the axial direction in orderto arrange the return spring, etc.

[0007] In view of the above, there exists a need for a multiple plateclutch device that overcomes the above-mentioned problems in the priorart. This invention addresses this need in the prior art as well asother needs, which will become apparent to those skilled in the art fromthis disclosure.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to conserve space in amultiple plate clutch device.

[0009] A multiple plate clutch device in accordance with a first aspectof the present invention has a first member, a second member, aplurality of first plates, a plurality of second plates, a piston, and areturn spring. The first member has a plurality of teeth aligned arounda circumference thereof. The second member is disposed so as to face thefirst member in a radial direction. The plurality of first plates hasengaging teeth that engage the plurality of teeth of the first member.The plurality of first plates is unable to rotate but able to move in anaxial direction relative to the first member. The plurality of secondplates is disposed alternately with respect to the plurality of firstplates in the axial direction. The second plates non-rotatably engagethe second member, and are able to move in the axial direction relativeto the second member. The piston presses the first plates and the secondplates together. The return spring is disposed inside a (groove betweenthe teeth of the first member and pushes the first plate that is closestto the piston toward the piston.

[0010] With this multiple plate clutch device, the clutch engages whenthe piston presses the first and second plates together. When the loadon the piston is released, the return spring applies a force on thepiston by way of the first plate that is closest to the piston andcauses the piston to separate from the first and second plates. As aresult, the multiple plate clutch device disengages. Since the returnspring is disposed inside a groove between the teeth of the firstmember, the space conventionally occupied by the return spring can beomitted.

[0011] A multiple plate clutch device in accordance with a second aspectof the present invention is the device of the first aspect, wherein thereturn spring is a flat spring.

[0012] This multiple plate clutch device is able to conserve space byusing a flat spring. The flat spring mentioned here is a spring madefrom a thin sheet material, that provides a spring effect. Morespecifically, the flat spring is made of a thin sheet having a thicknessof up to approximately 1 mm. The thin sheet is press worked into thedesired shape and given a spring effect.

[0013] A multiple plate clutch device in accordance with a third aspectof the present invention is the device of the second aspect, wherein thereturn spring is disposed between an engaging tooth of the first platethat is closest to the piston and an engaging tooth of the first platethat is farthest from the piston.

[0014] This multiple plate clutch device does not require a specialmember to support the return spring because the first plates support thereturn spring.

[0015] A multiple plate clutch device in accordance with a fourth aspectof the present invention is the device of any of the aforementionedaspects, wherein one end of the return spring is held in an engagingtooth of the first plate that is closest to the piston.

[0016] In this multiple plate clutch device, the first plate that isclosest to the piston determines the position of the return spring.

[0017] A multiple plate clutch device in accordance with a fifth aspectof the present invention is the device of the fourth aspect, wherein oneend of the return spring is held in the engaging tooth of the firstplate that is closest to the piston in such a manner that it cannot fallout.

[0018] With this multiple plate clutch device, the return spring and thefirst plate closest to the piston constitute a subassembly, makinghandling more convenient.

[0019] A multiple plate clutch device in accordance with a sixth aspectof the present invention is the device of the fifth aspect wherein aslit is provided in the engaging tooth of the first plate that isclosest to the piston. Further, the return spring has a claw that isheld in the slit provided in the engaging tooth of the first plate thatis closest to the piston.

[0020] A multiple plate clutch device in accordance with a seventhaspect of the present invention is the device of any of third throughsixth aspects, wherein the return spring has a flat section that abutsagainst an axially facing surface of the engaging tooth of the firstplate that is closest to the piston.

[0021] In this multiple plate clutch device, the orientation of thefirst plate that is closest to the piston is stable.

[0022] A multiple plate clutch device in accordance with an eighthaspect of the present invention is the device of any of third to seventhaspects, wherein the return spring has a curved part that contacts theengaging tooth of the first plate that is farthest from the piston.

[0023] In this multiple plate clutch device, the return spring candeflect smoothly in the axial direction when the clutch is engaged.

[0024] A multiple plate clutch device in accordance with a ninth aspectof the present invention is the device of eighth aspect, wherein thereturn spring has a projection whose movement in the radial direction isrestricted by the engaging tooth of the first plate that is farthestfrom the piston.

[0025] These and other objects, features, aspects, and advantages of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Referring now to the attached drawings which form a part of thisoriginal disclosure;

[0027]FIG. 1 is a cross-sectional schematic view illustrating aforward-reverse rotation device for a continuously variable transmissionin accordance with a preferred embodiment of the present invention;

[0028]FIG. 2 is a cross-sec-ional schematic view of a brake device ofthe forward-reverse rotation device of FIG. 1;

[0029]FIG. 3 is a partial elevational view in the direction of arrow IIIin FIG. 2;

[0030]FIG. 4 is an elevational view of an engaging tooth portion of afirst plate that is closest to a piston;

[0031]FIG. 5 is a cross-sectional view of a subassembly having the firstplate that is closest to the piston and at least one return spring;

[0032]FIG. 6 is an elevational view of the return spring;

[0033]FIG. 7 is an elevational view of the return spring in thedirection of arrow VII in FIG. 6;

[0034]FIG. 8 is a plan view of the return spring in the direction ofarrow VIII in FIG. 6;

[0035]FIG. 9 is an elevational view of an engaging tooth portion of anendplate in accordance with a second embodiment of the presentinvention;

[0036]FIG. 10 is a cross-sectional view of a subassembly and theendplate in accordance with the second embodiment of the presentinvention;

[0037]FIG. 11 is an elevational view of an engaging tooth section of afirst plate that is closest to a piston in accordance with the secondembodiment of the present invention;

[0038]FIG. 12 is a cross-sectional view of a return spring in accordancethe second embodiment of the present invention,

[0039]FIG. 13 is an elevational view of the return spring in thedirection of arrow XIII in FIG. 12;

[0040]FIG. 14 is a plan view of the return spring in the direction ofarrow XIV in FIG. 12;

[0041]FIG. 15 is a cross-sectional schematic view of a brake device inaccordance with a third embodiment of the present invention;

[0042]FIG. 16 is a plan view of a return spring in accordance with afourth embodiment of the present invention; and

[0043]FIG. 17 is a plan view of a return spring in accordance with afifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044]FIG. 1 shows a forward-reverse rotation device 1 for acontinuously variable transmission in accordance with a preferredembodiment of the present invention. The forward-reverse rotation device1 is disposed between a torque converter (not shown) to which power isdelivered from an engine (not shown) to a belt-type continuouslyvariable transmission (not shown). The forward-reverse rotation device 1transmits torque from an input shaft 2 that extends from the torqueconverter to an output shaft 3 that extends from the continuouslyvariable transmission. The forward-reverse rotation device 1 alsoreverses the direction of the rotational drive coming from the torqueconverter in order to allow the vehicle to move in reverse. Line O-O, inFIG. 1 is the rotational axis of the forward-reverse rotation device 1.

[0045] The forward-reverse rotation device 1 is equipped with aforward-reverse switching device 4 and a planetary gearset 5 thatswitches a power transmission path by the forward-reverse switchingdevice 4. The forward-reverse switching device 4 has a forward hydraulicclutch device 6 to which power is fed from the torque converter and areverse hydraulic brake device 7 that controls the planetary gearset 5.

[0046] The planetary gearset 5 is preferably a double pinion planet geartype gearset. The planetary gearset 5 is equipped with a sun gear 12, aring gear 13, a plurality of planet gears 14, and a planet carrier 15.The ring gear 13 that is concentric with the sun gear 12. The pluralityof planet gears 14 meshes with the gears 12 and 13. There are preferablysix planet gears 14. The planet carrier 15 supports the planet gears 14such that they can rotate about an axis. The forward hydraulic clutchdevice 6 couples and releases the input shaft 2 to and from the planetcarrier 15. The reverse hydraulic brake device 7 is a clutch device forsecuring and releasing the ring gear 13 to and from a transmission case21. As shown in FIG. 2, the brake device 7 has a piston 22 and a brakesection 23 (clutch section) that has a plurality of first and secondbrake plates 24, 25. The plurality of first and second brake plates 24,25 is pressed against one another by the piston 22.

[0047] The brake section 23 is disposed between an internalcircumferential surface section 31 (first member) that is a portion ofthe transmission case 21 and a ring gear 13 (second member). The brakesection 23 preferably contains the plurality of first brake plates 24and second brake plates 25. The brake plates 24, 25 are disposed in analternating manner along the axial direction. Each of the first andsecond brake plates 24, 25 is an annular plate member. A plurality ofengaging teeth 41 engages with teeth 35 of an internal circumferentialsurface section 31. The engaging teeth 41 are formed on an externalcircumferential section of the first brake plates 24. A plurality ofengaging teeth that engage with external teeth 13 a of the ring gear 13are formed on an internal circumferential section of the second brakeplates 25. Additionally, friction material is attached to both faces ofthe second brake plates 25. Here, “engaging teeth” refers to a pluralityof protrusions that project radially inward or outward from the internalor external circumferential edge of an annular plate.

[0048] With this arrangement, the first brake plates 24 can move freelyin the axial direction but cannot rotate with respect to thetransmission case 21. Further, the second plates 25 can move freely inthe axial direction but cannot rotate with respect to the ring gear 13.A brake plate among the plurality of first brake plates 24 that isfarthest from the piston 22 (rightmost brake plate in FIG. 2) functionsas an endplate and bears the load applied by the piston 22. Hereinafterthis plate is called an endplate 30. The endplate 30 is thicker than theother first brake plates 24. To the outside of the endplate 30 (i.e. theaxial side opposite the piston 22 side), a snap ring 27 for restrictingmovement in the axial direction is provided on the internalcircumferential surface section 31.

[0049] As seen in FIG. 3, the teeth 35 of the internal circumferentialsurface section 31 are lined up in a circumferential direction and eachhave a prescribed length in the axial direction. Grooves 36 are disposedcircumferentially between the teeth 35. The engaging teeth 41 of thefirst brake plates 24 fit into the grooves 36 such that thecircumferentially facing sides of the teeth 41 and the grooves 36 toucheach other. Further a slight gap is secured between the radially facingend faces of the engaging teeth 41 and the bottoms of the grooves 36.

[0050] Among the grooves 36 are a plurality of deep grooves 37 that aredeeper than the other grooves. The number of deep grooves 37 ispreferably between four to ten, inclusive. As seen in FIG. 2, among theengaging teeth 41 of the endplate 30 are engaging teeth 42 that arelonger than the other engaging teeth 41 in the radial direction andengage with the deep grooves 37. Meanwhile, among the engaging teeth 41of the first plate 29 closest to the piston 22 are engaging teeth 43that are longer than the other engaging teeth 41 in the radial directionand engage with the deep grooves 37. In short, large gaps are formedradially between the engaging teeth 41 of the three middle plates 24 andthe deep grooves 37. The engaging teeth 42, 43 of the outside plates 29,30 face each other through said large gaps inside the deep grooves 37.

[0051] As seen in FIGS. 9 and 3, return springs 28 have spring membersdisposed inside each deep groove 37. The return springs 28 apply a forceagainst the piston 22 in a direction of-separation from the brakesection 23 when the clutch is engaged. The return springs 28 move thepiston 22 when hydraulic pressure on the piston 22 is released. Thereturn springs 28 are disposed axially between the endplate 30 and thefirst plate 29 closest to the piston 22 such that they can flex in theaxial direction between the two plates 29, 30. More specifically, thereturn springs 28 are disposed inside the deep grooves 37 such that theylie between the deep grooves 37 and the engaging teeth of the threemiddle first plates 24 in the radial direction and between the engagingteeth 42 of the endplate 30 and the engaging teeth 43 of the first plate29 in the axial direction.

[0052] Referring to FIGS. 5, 6, and 8, the return springs 28 are flatsprings. The return springs 28 are relatively slender and lone in theaxial direction. The main surfaces of the springs face inward andoutward, respectively, in the radial direction. Each return spring 28has a main body 28 a. The width of the main body 28 a in thecircumferential direction is larger at the portion closest to the firstplate 29 than at the portion closest to the endplate 30 and bothcircumferentially facing edges of the former portion touch against thecircumferentially facing sides of the deep grooves 37. The entirety ofthe main body 28 a is curved smoothly so as to be convex in the outwardradial direction. The vertical cross sectional shape of the main body 28a is oval or semicircular, but a U or V shape is also acceptable. An endof the main body 28 a at the first plate 29 that is closest to thepiston 22 has a flat section 28 b and an engaging claw 28 c. The flatsection 28 b extends radially inward from the main body 28 a and touchesthe axially facing surface of one of the engaging teeth 43 of the firstplate 29. The flat section 28 b stabilizes the orientation of the firstplate 29. The engaging claw 28 c is a section formed on both sides ofthe flat section 28 b in a circumferential direction of the first plate29. The engaging claw 28 c extends in the axial direction so as to beinserted into a slit 43 a of one of the engaging teeth 43 shown in FIG.4. Therefore, the return spring 28 is unable to move with respect to thefirst plate 29 closest to the piston 22 in the rotational and radialdirections. Referring to FIG. 5, the tip of the engaging claw 28 c isalso bent such that it touches against the opposite axially facingsurface of one of the engaging teeth 43. As a result, the return spring28 is unable to move with respect to the first plate 29 closest to thepiston 22 in the axial direction. Thus, the plurality of return springs28 is fixed around the circumference of the first plate 29 closest tothe piston 22 and collectively therewith constitutes a singlesubassembly. This arrangement makes it easier to handle the plurality ofreturn springs 28 and simplifies the operation of installing theplurality of return springs 28 into the deep grooves 37.

[0053] As seen in FIGS. 2 and 5, the end of each return spring 28 at theendplate 30 has a bent section 28 d. The bent section 28 d is bent topoint in an inward radial direction and touches the axially facingsurface of the endplate 30.

[0054] The use of flat springs as the return springs makes it possibleto conserve space. The flat spring mentioned here is preferably madefrom a thin sheet material and provides a spring effect. Morespecifically, the flat spring is preferably made of a thin sheet havinga thickness of up to approximately 1 mm that is press worked into thedesired shape and thus given a spring effect. The spring load of a flatspring is determined by its thickness, width, and curvature.

[0055] The piston 22 is provided between the brake section 23 and alateral wall section 32 of the transmission case 11. The piston 22 is aroughly ring-shaped member. The piston 22 has on an externalcircumference a seal ring that is in sliding contact with the internalsurface 33 of the external circumferential wall of the transmission case21. The piston 22 also has on its internal circumference a seal ringthat is in sliding contact with the external surface 34 of the internalcircumferential wall of the transmission case 21. The piston 22 is madeof sheet metal and its external portion is a cylindrical section thatruns in the axial direction. The tip surface of the cylindrical sectioncan touch against the outer portion of the first plate 29 that isclosest to the piston 22. Thus, a cylinder chamber 45 is formed betweenthe piston 22 and the lateral wall section 32 of the transmission case21.

[0056] Operation

[0057] First the operation of the entire forward-reverse rotation device1 is explained.

[0058] When in Neutral

[0059] As seen in FIG. 1, when in a neutral state, neither the forwardhydraulic clutch device 6 nor the reverse hydraulic brake device 7 isengaged. Consequently, power inputted to the forward clutch device 6 isnot transmitted to the planetary gearset 5. Further, the rotation of theplanet carrier 15 is not braked. In this state, power from the torqueconverter is not transmitted to the belt-type continuously variabletransmission.

[0060] When in Forward

[0061] When in forward, hydraulic oil is supplied to the forwardhydraulic clutch device 6 and engages it. In short, the planet carrier15 is made to rotate integrally with the input shaft 2. Meanwhile,hydraulic oil is not supplied to the reverse hydraulic brake device 7and, consequently, the ring gear 13 of the planetary gearset 5 canrotate freely.

[0062] Here, power from the torque converter is transmitted to theoutput shaft 3 through clutch device 6 and the planet carrier 15 andoutputted to the belt-type continuous variable transmission. Thebelt-type continuously variable transmission rotates in the samedirection as the torque converter. Furthermore, in this state, all ofthe gears 12, 13, 14 of the planetary gearset 5 rotate synchronously asa single unit and torque from the torque converter is neither multipliednor reduced but transmitted directly to the output shaft 3.

[0063] When in Reverse

[0064] When in reverse, the forward hydraulic clutch device 6 isdisengaged and the reverse hydraulic brake device 7 is operated (brakingon). As a result, the rotation of the ring gear 13 of the planetarygearset 5 is prohibited.

[0065] In this state, power from the torque converter is transmittedfrom the sun gear 12 to double the planet gears 14 and the planetcarrier 15 and then to the output shaft 3 of the belt-type continuouslyvariable transmission. Since the ring gear 13 is prohibited fromrotating by the hydraulic brake device 7, the planet carrier 15 rotatesin direction opposing the sun gear 12. Thus, the output shaft 3 rotatesin a direction opposite its forward operation rotation.

[0066] Operation of Brake Device

[0067] Next, the operation of the brake device 7 is explained in detail.

[0068] Referring to FIG. 2, the piston 22 moves in the axial directiondue to the delivery of hydraulic oil into the cylinder chamber 45 andpushes the first and second brake plates 24, 25 against one another.When this occurs, the piston 22 pushes the first plate 29 that isclosest to the piston 22 with a force that is greater than the springload of the return spring 28. The return spring 28 is compressed in theaxial direction and, more specifically, curves so as to be convex in anoutward radial direction. Also, the return spring 28 bends smoothly dueto the bent section 28 d (FIG. 5). The configuration of the returnspring 28 makes it difficult for buckling or other problems to occur.Referring to FIG. 9, in this state, the return spring 28 applies areturn load against the first plate 29 and the piston 22 in thedirection of separation from the brake section 23. The piston 22 movesuntil the first and second brake plates 24, 25 touch against oneanother. The amount of this movement varies depending on the number offirst and second brake plates 24, 15, but it is roughly 1 mm.

[0069] When the supply of hydraulic pressure to the cylinder chamber 45ceases, the load applied against the piston 22 disappears. The firstplate 29 that is closest to the cylinder is pushed by return spring 28and separates from the brake section 23, thus pushing against the piston9. As a result, the plates 24, 25 separate from each other and theclutch or brake device 7 disengages.

[0070] Effects

[0071] As discussed previously, since the return springs 28 are disposedinside the deep grooves 37 of the internal circumferential surfacesection 31, the conventional retaining plate, snap ring, and groove forthe snap ring are eliminated. Also, the extra space occupied byconventional return springs is not necessary.

[0072] Improved compactness makes it easier to design the transmission.Since the extra space normally occupied by the returns springs iseliminated, the entire transmission, including the housing, is morecompact and thus lighter in weight.

[0073] Since the snap ring and retaining plate parts are unnecessary,the device is less expensive. Cost is also lowered by the reduction inweight.

[0074] Alternate Embodiments

[0075] Referring now to FIGS. 9 to 17, a multiple plate clutch device inaccordance with alternate embodiments of the present invention will nowbe discussed. In view of the similarities between the previousembodiment and the alternate embodiments, the components or parts of thealternate embodiments that have the same function of the correspondingcomponents or parts of the previous embodiment are being given identicalreference numerals. Moreover, the explanations of components or partsand operations of the alternate embodiments that are similar tocomponents or parts and operations of the first embodiment will beomitted. Only components and operations of the alternate embodimentsthat are different in structure and function from the previousembodiment will be explained herein. In other words, the basic structureof the alternate embodiments is the same as that of the firstembodiment. Only the differences are described here.

[0076] Second Embodiment

[0077] Referring to FIG. 10 the middle portion of a main body 38 a ofeach return spring 38 is of a rectangular shape that extends in an axialdirection and both ends thereof spread in both circumferentialdirections. Both circumferentially facing edges of both ends of thereturn spring 38 touch against both circumferentially facing sides ofthe deep groove 37.

[0078] The end of the return spring 38 that is closer to an endplate 55is held by the endplate 55. Thus, its movement in the radial direction,particularly the inward radial direction, is restricted. Morespecifically, at one end of the return spring 38, a projection 38 fextends in the axial direction. The end is formed on a portion of a bentsection 38 d that is in the middle with respect to the circumferentialdirection of the device. Meanwhile, as shown in FIG. 9, a notch 55 b isprovided in the radially outward-facing end of an engaging tooth 55 a ofthe endplate 55. The notch 55 b opens in an outward radial direction.The projection 38 f of the return spring 38 is held in the notch 55 band its movement in the inward radial direction is restricted. As aresult, the position of the end of the return spring 38 that is closerto the endplate is determined and the return spring 38 is prevented frommoving in the inward radial direction or popping out of position.

[0079] As seen in FIG. 10, the end of the return spring 38 at a firstplate 54 that is closest to the piston 22 has a flat section 38 b and aprojection 38 c. The projection 38 c extends in the axial direction andis formed on a middle portion of the flat section 38 b. Meanwhile, asshown in FIG. 11, a slit 54 b is formed on am engagement tooth 54 a ofthe first plate 54 that is closest to the piston 22. The projection 38 cextends through and beyond the slit 54 b in the axial direction. As seenin FIG. 10, a spring back section 38 e is also formed on the projection38 c by cutting and bending upward a portion of the projection 38 c. Thespring back section 38 e touches against a piston facing face of theengaging tooth 54 a and prevents the projection 38 c from coming out.Thus, the return spring 38 is secured to the first plate 54 that isclosest to the piston 22 and forms a subassembly. As a result, thehandling and assembly of both members is easier. More particularly, aplurality of return springs 38 is secured to the first plate 54 that isclosest to the piston 22 in advance. During assembly, it is sufficientto attach simply the first plate 54 to the transmission case 21. It isnot necessary to arrange each return spring 38 inside the grooves 37 oneby one.

[0080] When a return spring 38 is secured to the first plate 54, thespring back section 38 e is formed inside the slit 54 b as theprojection 38 c is passed into the slit 54 b. At the position where theflat section 38 b contacts the axially facing surface of the engagingtooth 54 a, the spring back section pops out of the slit 54 b andtouches against the opposite axially facing surface of the engagingtooth 54 a.

[0081] Third Embodiment

[0082] This embodiment has the same basic structure as the firstembodiment. Referring to FIG. 15, a dish plate or Belleville spring 26is disposed between the piston 22 and the first plate 29 is closest tothe piston 22. The Belleville spring 26 serves as a damping spring forabsorbing the shock that occurs when the piston 22 engages the brakesection 23. The Belleville spring 26 is an annular disk member andpreferably is conical in shape. The internal circumferential edge of theBelleville spring 26 is supported on the first plate 29 and the externalcircumferential edge is supported on a pushing section of the piston 22.

[0083]FIG. 15 shows the disengaged condition of the clutch or reversehydraulic brake device 7. The piston 22 is pushed away from the endplate30 by the return spring 28 through the first plate 29 and the Bellevillespring 26. In this condition, the Belleville spring 26 is flexed inaccordance with the spring load of the return spring 28.

[0084] The piston 22 moves in an axial direction and pushes the firstand second brake plates 24, 25 against one another when hydraulic oil issupplied to the cylinder chamber 45. Here, the piston 22 pushes thefirst brake plate 29 adjacent the Belleville spring 26 through theBelleville spring 26 with a force larger than the spring load of thereturn spring 28.

[0085] The piston 22 moves until the first and second brake plates 24,25 touch one another. After the plates 24, 25 contact one another thepiston 22 moves toward the endplate 30 until the Belleville spring 26 isflattened. In this condition, the load applied on the brake section 23is equal to the difference between the spring load of the Bellevillespring 26 and the spring load of the return spring 28. The movementstroke of the piston 22 in this embodiment is larger than that in thefirst embodiment by the distance through which the Belleville spring 26flexes, but the movement stroke of the return spring 28 is the same asin the first embodiment. Therefore, similar to the first embodiment, themovement stroke of the return spring 28 can be held to a very smallamount because the return spring 28 does not act on the piston 22directly. Rather, the return spring 28 acts on the first plate 29, whichis closest to the piston among the brake plates and disposed on the thebrake section 23 side of Belleville spring 26. In a conventionalarrangement the return spring has a large stroke, making it difficult toprovide a return spring with sufficient performance.

[0086] Since the spring load of the Belleville spring 26 is generallyset to be larger than the spring load of the return spring 28, there isno large effect on the shock absorbing performance of the Bellevillespring 26 when the return spring 28 pushes the Belleville spring 26.

[0087] Fourth Embodiment

[0088] A return spring 61 shown in FIG. 16 has basically the samestructure as the return spring 28 shown in FIG. 8 of the firstembodiment except that return prevention turned-back parts 61 e areprovided on the tips of two claws 61 c. The turned-back parts 61 eextend inward toward each other in the circumferential direction.

[0089] The claws 61 c spread apart in a circumferential direction whenthey are inserted into a slit 43 a but return toward each othersimultaneously when a flat section 61 b touches against an engagingtooth. When the claws 61 c return, turned-back parts 61 e touch againstthe opposite axially facing surface of the engaging tooth.

[0090] Fifth Embodiment

[0091] A return spring 62 shown in FIG. 17 has basically the samestructure as the return spring 38 shown in FIG. 14 of the secondembodiment except that a projection or claw 62 c is divided into twosections in the radial direction and a return prevention turned-backpart 62 e is provided on the tip of each of the two sections. Theturned-back parts 62 e extend outward and away from each other in thecircumferential direction.

[0092] The two sections of the claw 62 c contract inward in thecircumferential direction when they are inserted into the slit 54 b butreturn simultaneously outward in the circumferential direction when aflat section 62 b touches against an engaging tooth. When the clawsections return, the turned-back parts 62 e touch against the oppositeaxially facing surface of the engaging tooth.

[0093] Since the present invention can be applied to all types ofmultiple plate clutches, it is not limited to the embodiments describedheretofore. Furthermore, when the invention is used in a brake device,it is not necessary to use a special structure to prevent problemsresulting from centrifugal force because centrifugal force does not acton the return spring. Particularly in the case of a brake device, thespring load of the return spring is preferably 50 kg and the degree ofprecision does not need to be particularly high.

[0094] In a multiple plate clutch device in accordance with the presentinvention, the extra space occupied by a conventional return spring inthe prior art can be eliminated because the return spring is disposedinside a groove between the teeth of a first member.

[0095] The terms of degree such as “substantially,” “about,” and“approximately” as used herein mean a reasonable amount of deviation ofthe modified term such that the end result is not significantly changed.These terms should be construed as including a deviation of at least ±5%of the modified term if this deviation would not negate the meaning ofthe word it modifies.

[0096] While only selected embodiments have been chosen to illustratethe present invention, it will be apparent to those skilled in the artfrom this disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing description of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

What is clamed is:
 1. A multiple plate clutch device comprising: a firstmember having a plurality of teeth aligned around a circumferencethereof; a second member being disposed to face said first member in theradial direction; a plurality of first plates having engaging teeth thatengage with the plurality of teeth of said first member, said pluralityof first plates being non-rotatable and axially movable relative to saidfirst member; a plurality of second plates being disposed alternatelywith respect to said plurality of first plates in an axial direction andnon-rotatably and axially movably engaging with said second memberrelative to said second member; a piston being configured to press saidplurality of first plates and said plurality second plates together; anda return spring being disposed inside a groove between said teeth ofsaid first member, said return spring being configured to push one ofsaid plurality of first plates being closest to said piston toward saidpiston.
 2. The multiple plate clutch device according to claim 1,wherein said return spring is a flat spring.
 3. The multiple plateclutch device according to claim 2, wherein said return spring isdisposed between an engaging tooth of said one of said plurality offirst plates being closest to said piston and an engaging tooth of oneof said plurality of first plates being farthest from said piston. 4.The multiple plate clutch device according to claim 3, wherein an end ofsaid return springy is held in said engaging tooth of said one of saidplurality of first plates being closest to said piston.
 5. A multipleplate clutch device according to claim 4, wherein said one end of saidreturn spring is fixedly connected to said engaging tooth of said one ofsaid plurality of first plates being closest to said piston in such amanner that said return spring cannot fall out.
 6. The multiple plateclutch device according to claim 5, wherein a slit is provided in saidengaging tooth of said one of said plurality of first plates beingclosest to said piston and said return spring has a claw that isconnected to said slit provided in said engaging teeth of said one ofsaid plurality of first plates being closest to said piston.
 7. Themultiple plate clutch device according to claim 6, wherein said returnspring has a flat section that abuts an axially facing surface of saidengaging tooth of said one of said plurality of first plates beingclosest to said piston.
 8. The multiple plate clutch device according toclaim 7, wherein said return spring has a curved part that contacts saidengaging tooth of said one said first plate being farthest from saidpiston.
 9. The multiple plate clutch device according to claim 8,wherein said return spring has a projection whose movement in the radialdirection is restricted by said engaging tooth of said first plate thatis farthest from said piston.
 10. A torque transmission systemcomprising: a torque converter input shaft; a continuously variabletransmission output shaft; and a forward-reverse rotation device beingconfigured to transmit torque from said input shaft to said outputshaft, said forward-reverse rotation device comprising, aforward-reverse switching device having a forward hydraulic clutchdevice being configured to receive torque from said input shaft, and aplanetary gearset being configured to switch a power transmission pathby said forward-reverse switching device, said planetary gearset beingconfigured to be controlled by a multiple plate clutch device, saidmultiple plate clutch device comprising, a first member having aplurality of teeth aligned around a circumference thereof, a secondmember being disposed to face said first member in the radial direction,a plurality of first plates having engaging teeth that engage with theplurality of teeth of said first member, said plurality of first platesbeing non-rotatable and axially movable relative to said first member, aplurality of second plates being disposed alternately with respect tosaid plurality of first plates in an axial direction and non-rotatablyand axially movably engaging with said second member relative to saidsecond member, a piston being configured to press said plurality offirst plates and said plurality second plates together, and a returnspring being disposed inside a groove between said teeth of said firstmember, said return spring being configured to push one of saidplurality of first plates being closest to said piston toward saidpiston.
 11. The torque transmission system according to claim 10,wherein said return spring is a flat spring.
 12. The torque transmissionsystem according to claim 11, wherein said return spring is disposedbetween an engaging tooth of said one of said plurality of first platesbeing closest to said piston and an engaging tooth of one of saidplurality of first plates being farthest from said piston.
 13. Thetorque transmission system according to claim 12, wherein an end of saidreturn spring is held in said engaging tooth of said one of saidplurality of first plates being closest to said piston.
 14. A torquetransmission system according to claim 13, wherein said one end of saidreturn spring is fixedly connected to said engaging tooth of said one ofsaid plurality of first plates being closest to said piston in such amanner that said return spring cannot fall out.
 15. The torquetransmission system according to claim 14, wherein a slit is provided insaid engaging tooth of said one of said plurality of first plates beingclosest to said piston and said return spring has a claw that isconnected to said slit provided in said engaging teeth of said one ofsaid plurality of first plates being closest to said piston.
 16. Thetorque transmission system according to claim 15, wherein said returnspring has a flat section that abuts an axially facing surface of saidengaging tooth of said one of said plurality of first plates beingclosest to said piston.
 17. The torque transmission system according toclaim 16, wherein said return spring has a curved part that contactssaid engaging tooth of said one said first plate being farthest fromsaid piston.
 18. The torque transmission system according to claim 17,wherein said return spring has a projection whose movement in the radialdirection is restricted by said engaging, tooth of said first plate thatis farthest from said piston.
 19. The torque transmission systemaccording to claim 11, wherein an elastic member is arranged betweensaid piston and said one of said plurality of first plates being closestto said piston.
 20. The torque transmission system according to claim14, wherein said engaging tooth of said one of said plurality of firstplates being closest to said piston is configured to have an apertureand said one end of said return spring is configured to have a firstprojection that is inserted into said aperture in a first direction,said one end of said return spring is configured to have a second tohave a second projection that extends in a second direction, said firstdirection and said second direction are substantially perpendicular.